CN113852425A - Blind carrier phase shift compensation method and device in pulse amplitude modulation system - Google Patents

Abstract

Embodiments of the present invention provide a blind carrier phase shift compensation method and device in a pulse amplitude modulation PAM system, by decomposing the PAM signal of each subcarrier into a first real part signal and a first imaginary part signal; A real part signal and the imaginary part signal are filtered respectively to obtain a second real part signal and a second imaginary part signal; the phase shift is calculated according to the second imaginary part signal and the second real part signal; The above-mentioned phase shift compensates the subcarrier frequency; the blind carrier phase shift compensation method is suitable for the multi-band PAM optical communication system and can accurately calculate the phase offset of the carrier, and then perform phase shift compensation on the carrier according to the phase offset; Thus, the influence of the carrier phase shift caused by the mismatch between the factor carrier frequency and the AWG reference clock on the system is reduced, and the performance of the optical communication system is improved.

Description

Method and device for blind carrier phase shift compensation in pulse amplitude modulation system

technical field

The embodiments of the present invention relate to, but are not limited to, the field of optical communications, and specifically relate to, but are not limited to, a method and device for blind carrier phase shift compensation in a pulse amplitude modulation PAM system.

Background technique

Nowadays, the research of optical communication has attracted more and more people's attention. In view of the research hotspot of networks, we hope that visible light communication can provide the function of supporting multi-user high-speed access. Therefore, multi-band visible light communication systems based on frequency division multiplexing (FDM) or wavelength division multiplexing (WDM) and advanced modulation formats have received extensive attention. Pulse Amplitude Modulation (PAM) has a simple structure and low computational complexity. More flexible, enabling higher transfer rates. However, carrier phase drift is a critical issue for high-speed multi-band PAM optical communication systems, which is caused by the mismatch between the signal subcarrier frequency and the arbitrary waveform generator (AWG) reference clock. In addition, the high sampling requirements of multi-band systems increase the symbol length, which makes the transmitted symbols more sensitive to phase shifts. Therefore, how to perform carrier phase estimation and compensation in the visible light communication system plays a very important role in improving the system performance.

Decision assistance and decision feedback mechanisms based on digital phase-locking loop (PLL) are widely used for carrier phase recovery in radio frequency communication systems. Since the phase of the RF carrier changes slowly, a digital phase-locked loop can keep up with the phase change. In the high-speed optical communication system, the phase change speed of the optical carrier is much faster than that of the radio frequency carrier, and only the phase recovery based on feedforward can be realized by parallel processing and pipeline structure in practice. Therefore, the phase estimation algorithm is a very important link in coherent optical communication. In the past carrier phase estimation compensation algorithms, the Blind Phase Search (BPS) method of M-order modulation and the Viterbi&Viterbi algorithm are two classic compensation algorithms.

The basic block diagram of the BPS algorithm and the improved BPS algorithm is shown in Figure 1(a)(b), which adopts a pure feedforward structure.

Put the sampled symbols r _k containing phase noise on the constellation diagram plane with B test phases φ _b

如式Rotate, test phase

as

The parameter B directly affects the accuracy of the algorithm. The larger B is, the more accurate the phase noise estimation is, but the greater the amount of calculation and the more complex the algorithm.

计算出频偏Δv：For the V&V algorithm, first estimate the frequency offset of the signal. The frequency offset will cause the phase difference between adjacent samples. By estimating the phase difference between consecutive samples

Calculate the frequency offset Δv:

The received signal Sn _is multiplied by the complex conjugate Sn _-1 of its preceding signal. The phase of the resulting complex number d _n is the phase difference of the two symbols:

where θ _n -θ _n-1 ≈0.

Removes encoded information contained in the phase of the signal. For the phase shift keying signal, it is only necessary to perform the M power on the complex signal, and M is also the number of points in the constellation diagram. For example, the quadrature phase shift keying signal (QPSK) only needs to power the complex number obtained before:

对QPSK信号来说，b_n∈{0，±π/2，±π}。因此有exp(j×4b_n)＝1。in,

For a QPSK signal, _bn ∈ {0, ±π/2, ±π}. Hence exp( _j ×4bn )=1.

After removing the frequency offset noise, the signal expression can be written as:

S′ _n =exp(j(α _n +θ _n )) (6)

These methods were originally designed because the symbol signal pulse (M-QAM) has rich phase information. However PAM is a one-dimensional modulation with only two phases, furthermore, all symbols carried on the same band can be considered to have the same phase shift. Therefore, conventional blind carrier phase estimation (CPE) algorithms may not be suitable for our multi-band PAM optical communication system.

Therefore, it is necessary to provide a carrier phase estimation compensation method, which can be applied to a multi-band PAM optical communication system and can accurately estimate the phase offset of the carrier, thereby improving the overall performance of the system.

SUMMARY OF THE INVENTION

The embodiments of the present invention provide a blind carrier phase shift compensation method and device, and the main technical problem to be solved is that the CPE algorithm in the prior art cannot solve the problem of carrier phase shift in a multi-band PAM optical communication system.

In order to solve the above technical problem, an embodiment of the present invention provides a blind carrier phase shift compensation method in a PAM system, including:

Decomposing the PAM signal of each subcarrier into a first real part signal and a first imaginary part signal;

Filtering the first real part signal and the imaginary part signal respectively to obtain a second real part signal and a second imaginary part signal;

calculating a phase shift according to the second imaginary part signal and the second real part signal;

The carrier frequency is compensated according to the phase shift.

An embodiment of the present invention also provides a blind carrier phase shift compensation device in a PAM system, including:

a signal decomposition module for decomposing the PAM signal of each subcarrier into a first real part signal and a first imaginary part signal;

a filtering module, configured to filter the first real part signal and the imaginary part signal respectively to obtain a second real part signal and a second imaginary part signal;

a phase shift calculation module, configured to calculate a phase shift according to the second imaginary part signal and the second real part signal;

The phase shift compensation module is used for compensating the carrier frequency according to the phase shift.

technical effect

According to a blind carrier phase shift compensation method and device provided by the embodiments of the present invention, the PAM signal of each subcarrier is decomposed into a first real part signal and a first imaginary part signal; The imaginary part signals are filtered respectively to obtain a second real part signal and a second imaginary part signal; a phase shift is calculated according to the second imaginary part signal and the second real part signal; frequency compensation; in some implementation processes, the blind carrier phase shift compensation method can be implemented, including but not limited to, not only applicable to multi-band PAM optical communication systems, but also can accurately calculate the phase offset of the sub-carrier, and then according to The phase offset compensates the phase shift of the sub-carriers; thus, the influence of the carrier phase shift caused by the mismatch between the factor carrier frequency and the AWG reference clock on the system is reduced, and the performance of the optical communication system is improved.

Other features of the present invention and corresponding benefits are set forth in later parts of the specification, and it should be understood that at least some of the benefits will become apparent from the description of the present specification.

Description of drawings

Fig. 1 is the basic block diagram of the existing BPS algorithm and the improved BPS algorithm;

FIG. 2 is a flowchart of a blind carrier phase shift compensation method according to Embodiment 1 of the present invention;

3 is a schematic diagram of a blind carrier phase shift compensation device according to Embodiment 2 of the present invention;

4 is a constellation diagram of a multi-band PAM-8 according to Embodiment 3 of the present invention;

5 is an explanatory diagram of a blind carrier phase shift compensation method according to Embodiment 3 of the present invention;

FIG. 6 is a flowchart of a blind carrier phase shift compensation method according to Embodiment 3 of the present invention;

Fig. 7 is the geometric projection method experiment result diagram of the third embodiment of the present invention;

FIG. 8 is a multi-band PAM optical communication system according to Embodiment 4 of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1:

In order to solve the problem that the CPE algorithm in the prior art cannot solve the phase shift problem of the carrier in the multi-band PAM optical communication system, the embodiment of the present invention provides a blind carrier phase shift compensation method in the PAM system. With reference to FIG. 2, the method includes the following step:

S101: Decompose the PAM signal of each subcarrier into a first real part signal and a first imaginary part signal;

S102: Perform filtering processing on the first real part signal and the imaginary part signal respectively to obtain a second real part signal and a second imaginary part signal;

S103: Calculate a phase shift according to the second imaginary part signal and the second real part signal;

S104: Compensate the carrier frequency according to the phase shift.

Through the above steps, the blind carrier phase shift compensation method is not only suitable for the multi-band PAM optical communication system, but also can accurately calculate the phase offset of the subcarrier, and then perform phase shift compensation on the subcarrier according to the phase offset; The influence of the carrier phase shift caused by the mismatch between the factor carrier frequency and the AWG reference clock on the system is eliminated, and the performance of the optical communication system is improved.

In some inventive embodiments, the above S101 includes:

Multiply the PAM signal by the cosine function cos(2πft) to obtain the first real part signal;

Multiply the PAM signal by the sine function sin(2πft) to obtain the first imaginary part signal;

Both the frequency in the cosine function and the frequency in the sine function are equal to the frequency in the PAM signal.

It can be understood that the real axis component and the imaginary axis component of the PAM signal can be obtained by multiplying the PAM signal of each subcarrier by the cos and sin functions of the corresponding subcarrier frequency respectively.

In some inventive embodiments, the above S102 includes:

Signals within a preset frequency range in the real part signal and the imaginary part signal are filtered out by a low-pass filter.

It can be understood that the real part signal and the imaginary part signal respectively pass through a low-pass filter to filter out the high frequency signal in the signal, so as to obtain the baseband signal.

In some inventive embodiments, the above S103 includes:

The calculating the phase shift according to the second imaginary part signal and the second real part signal includes:

The phase shift is calculated using the following formula:

为相移，Q′(k)为所述第二虚部信号，I′(k)为所述第二实部信号， k为传输符号的长度。in,

is the phase shift, Q'(k) is the second imaginary signal, I'(k) is the second real signal, and k is the length of the transmitted symbol.

It can be understood that the phase shift of the sub-carrier can be obtained by the inverse trigonometric function of the ratio of I′ ₁ (k) and Q′ ₁ (k), and the obtained phase shift is generally between -π/2 and π/2.

In some inventive embodiments, the above S103 includes:

The calculating the phase shift according to the second imaginary part signal and the second real part signal further includes:

The phase shift is calculated using the following formula:

为相移，Q′(k)为所述虚部信号，I′(k)为所述实部信号，k为传输符号的长度，K为传输符号的总长度。in,

is the phase shift, Q'(k) is the imaginary part signal, I'(k) is the real part signal, k is the length of the transmission symbol, and K is the total length of the transmission symbol.

It can be understood that the carrier phase shift of the high frequency sub-carrier may exceed -π/2 to π/2, and in this case, a more accurate phase shift can be obtained by judging the symbol. Since all transmitted symbols on the same subcarrier have the same phase shift, a phase shift average can be used, which can be calculated by calculating the root mean square of all symbols on the same subcarrier. The phase shift compensation can be performed by adding the calculated phase shift mean value to the carrier frequency.

The blind carrier phase shift compensation method provided by the embodiment of the present invention makes the blind carrier phase shift compensation method suitable for the multi-band PAM optical communication system and can accurately calculate the phase offset of the carrier, and then phase the carrier according to the phase offset. Shift compensation; thereby reducing the influence of the carrier phase shift caused by the mismatch between the factor carrier frequency and the AWG reference clock on the system, and improving the performance of the optical communication system.

Embodiment 2:

In order to solve the problem that the CPE algorithm in the prior art cannot solve the phase shift problem of the carrier in the multi-band PAM optical communication system, an embodiment of the present invention provides a blind carrier phase shift compensation device in the PAM system. With reference to FIG. 3, the device includes the following Module:

a signal decomposition module for decomposing the PAM signal of each subcarrier into a first real part signal and a first imaginary part signal;

a filtering module, configured to filter the first real part signal and the imaginary part signal respectively to obtain a second real part signal and a second imaginary part signal;

a phase shift calculation module, configured to calculate a phase shift according to the second imaginary part signal and the second real part signal;

The phase shift compensation module is used for compensating the carrier frequency according to the phase shift.

Through the above device, the blind carrier phase shift compensation device is not only suitable for the multi-band PAM optical communication system, but also can accurately calculate the phase offset of the carrier, and then perform phase shift compensation on the subcarriers according to the phase offset; The performance of the optical communication system is improved by factoring the effect of the carrier phase shift caused by the mismatch between the carrier frequency and the AWG reference clock on the system.

In some embodiments, the above signal decomposition module is specifically configured to: multiply the PAM signal by a cosine function cos(2πft) to obtain the first real part signal; multiply the PAM signal by a sine function sin(2πft) The first imaginary part signal is obtained by multiplying; the frequency in the cosine function and the frequency in the sine function are both equal to the frequency in the PAM signal.

It can be understood that the real axis component and the imaginary axis component of the PAM signal can be obtained by multiplying the PAM signal of each subcarrier by the cos and sin functions of the corresponding subcarrier frequency respectively.

In some embodiments, the above filtering module is specifically configured to filter out signals within a preset frequency range in the real part signal and the imaginary part signal through a low-pass filter.

It can be understood that the real part signal and the imaginary part signal respectively pass through a low-pass filter to filter out the high frequency signal in the signal, so as to obtain the baseband signal.

In some embodiments, the above-mentioned phase shift calculation module is specifically used to calculate the phase shift using the following formula:

为相移，Q′(k)为所述第二虚部信号，I′(k)为所述第二实部信号， k为传输符号的长度。in,

is the phase shift, Q'(k) is the second imaginary signal, I'(k) is the second real signal, and k is the length of the transmitted symbol.

It can be understood that the phase shift of the sub-carrier can be obtained through the inverse trigonometric function of the ratio of I′ ₁ (k) and Q′ ₁ (k), and the obtained phase shift is between -π/2 and π/2.

In some embodiments, the above-mentioned phase shift calculation module is specifically used to calculate the phase shift using the following formula:

The phase shift is calculated using the following formula:

为相移，Q′(k)为所述虚部信号，I′(k)为所述实部信号，k为传输符号的长度，K为传输符号的总长度。in,

is the phase shift, Q'(k) is the imaginary part signal, I'(k) is the real part signal, k is the length of the transmission symbol, and K is the total length of the transmission symbol.

It can be understood that the carrier phase shift of the high frequency sub-carrier may exceed -π/2 to π/2, and in this case, a more accurate phase shift can be obtained by judging the symbol. Since all transmitted symbols on the same subcarrier have the same phase shift, a phase shift average can be used, which can be calculated by calculating the root mean square of all symbols on the same subcarrier.

In some embodiments, the above-mentioned phase shift compensation module is specifically configured to add the calculated phase shift or the average value of the phase shift to the carrier frequency to perform phase shift compensation.

The blind carrier phase shift compensation device provided by the embodiment of the present invention is not only suitable for a multi-band PAM optical communication system, but also can accurately calculate the phase offset of the carrier, and then perform phase shift compensation on the carrier according to the phase offset; The influence of the carrier phase shift caused by the mismatch between the factor carrier frequency and the AWG reference clock on the system is eliminated, and the performance of the optical communication system is improved.

Embodiment three:

In order to better understand the blind carrier phase shift compensation method provided by the embodiments of the present invention, the above blind carrier phase shift compensation method is further described below with reference to specific application scenarios.

Please refer to FIGS. 4-5 ; wherein, FIG. 4 is a constellation diagram of a multi-band PAM-8, and FIG. 5 is an explanatory diagram of a blind carrier phase shift compensation method.

The kth transmission coincidence in N subcarriers can be expressed as:

a _k is the amplitude of the PAM-8 signal, k is the length of the transmitted symbols in the nth subcarrier, and K is the total length of the transmitted symbols in the subcarriers.

The received PAM transmission symbols can be approximated as:

是第n个子载波上第k个传输符号的相移。Among them, N ₀ (k) is the AWGN signal,

is the phase shift of the kth transmission symbol on the nth subcarrier.

Then adopt the blind carrier phase shift compensation method provided by the implementation of the present invention to perform phase compensation on each transmission line in each subcarrier, which includes the following steps in conjunction with FIG. 6 :

S201: Decompose the PAM signal into a real component and an imaginary component;

As shown in (a) of Fig. 5, multiply each sub-carrier signal by the cos(2πf _n t) and sin((2πf _{n t} ) functions of the corresponding sub-carrier frequency, respectively, to obtain the real-axis component of the distortion signal In ( k) and the imaginary axis component _Qn (k).

S202: Filter out high-frequency signals to obtain baseband signals;

)。As shown in (b) of Figure 5, the Fourier transform (FTT) is used to receive the signal, and a low-pass filter is used to filter out the high-frequency components of the signal, and then the inverse Fourier transform (IFTT) is used to transmit the signal, and finally the baseband signal is obtained. The real axis component I' _n (k) and the imaginary axis component Q' _n (k) of . (in,

).

S203: Find the phase shift:

As shown in (c) of FIG. 5 , the phase shift of the sub-carrier is obtained by calculating the inverse trigonometric function of the ratio of the filtered I-channel and Q-channel signals. The phase obtained by the inverse trigonometric function is between -π/2 and π/2, and the carrier phase shift of the high frequency subcarrier may exceed this range, so it is necessary to judge the sign to obtain a more accurate degree of phase deviation. Since all symbols on the same subcarrier have the same phase shift, the mean phase shift can be estimated by calculating the root mean square of all symbols on the same subcarrier.

The phase-shift mean expression is as follows:

and,

S204: Compensate for phase shift:

之后对多带PAM-8信号进行解调解码以恢复原始二进制比特流。As shown in (d) in Figure 5, the calculated average phase shift is added to the carrier frequency for phase shift compensation; the kth transmission symbol on the nth subcarrier after the phase offset compensation is expressed as:

The multi-band PAM-8 signal is then demodulated and decoded to restore the original binary bit stream.

Figure 7 shows the experimental results of the geometric projection method. It can be seen from the experimental results that the M-PAM signal will further evolve into an ellipsoid constellation point distribution due to the influence of amplitude noise and phase noise at the receiver. This signal has completely deviated from the real axis and has phase rotation in the I-Q space. At this time, according to the principle of geometric projection, the statistical distribution of constellation points can be projected to the real axis and the imaginary axis respectively, and the projection root mean square of all symbols on the real axis and the imaginary axis can be calculated. The ratio of the roots gives a direct result of the phase shift. The parameters in the calculation formulas of the steps in the blind carrier phase shift compensation method in the embodiment of the present invention do not involve the number of carriers, the size of the subcarriers in the multiband, and the modulation order of the M-PAM; therefore, the method is different from the multiband modulation order. The number of bands, the subcarrier size in multi-band and the modulation order of M-PAM are irrelevant. Therefore, it can be applied to a multi-band M-PAM system to achieve uniform phase estimation in the case of unknown system modulation order.

Embodiment 4:

The implementation of the present invention also provides a visible light communication system for compensating for the phase shift of sub-carriers, as shown in FIG. 8 , including a transmitting end and a receiving end.

The sending end includes data preprocessing, an input module, a modulator and an LED light. The input module is used to receive the information to be sent; the modulator modulates the information to be sent into the visible light emitted by the LED light.

Data preprocessing, the data stream can perform bit loading on each subcarrier according to the signal-to-noise ratio (SNR), subcarriers with high SNR can support PAM8 or PAM16, and even higher order signals such as GS or PS PAM10, and subcarriers with low SNR support PAM4, or a lower OOK signal, multi-band can make full use of the signal-to-noise ratio, and provide different modulation orders for different SNRs to maximize system capacity. On the other hand, multi-band can finely divide the spectrum, which is beneficial to multi-user multiple access and user dynamic bandwidth allocation.

In the input module, the multi-user signal streams are loaded on different sub-carriers through weighted pre-equalization, and then directly modulated on the LED or LD to transmit in the form of visible light.

The modulator performs modulation of the transmitted data.

LED lights are used for the emission of light signals.

The receiving end includes a photoelectric detector, a signal processing module, a demodulator and an output module.

The photodetector is used to convert the visible light into an electrical signal and output it to the demodulator for demodulation. The demodulator demodulates the electrical signal. The output module is used for outputting the information demodulated by the demodulator.

The photodetector converts the optical signal into an electrical signal after receiving it by Pin, and then performs further signal processing at the back end.

The signal processing module, the signal is first resampled and synchronized, and then the phase shift compensation is performed by the blind carrier phase shift compensation method in the first embodiment of the present invention, and then normalized and down-sampled after filtering in the frequency domain, and then the signal passes through S-MCMMA adaptive filtering to further compensate for the loss of the signal.

The demodulator is used to demodulate the PAM signal.

The output module is used to transmit the information of different carriers to the corresponding users.

The blind carrier phase shift compensation method according to the embodiment of the present invention can be applied to a multi-band Nyquist PAM-8 high-speed visible light communication system. The specific implementation process is as follows:

As shown in Figure 8, data preprocessing is performed first. Data 1, 2, and 3 represent data on different sub-carriers. After PAM-8 modulation and up-sampling, Nyquist filtering is performed to help reduce the signal. Impairments during transmission are then modulated onto subcarriers of different frequencies through weighted pre-equalization. The information is generated by an arbitrary waveform generator, and then modulated on the red LED through pre-equalization and amplification. The optical signal is transmitted by the LED through the channel and received by the receiver.

The receiving end receives the optical signal by the photodiode and converts it into an electrical signal, and the electrical signal is amplified by the amplifier and then processed for the back-end signal. The signal is firstly compensated for phase shift by the blind carrier phase shift compensation method in each embodiment of the present invention, and then the sub-carriers of the corresponding users are filtered out in the frequency domain, and then normalized, down-sampled and equalized by S-MCMMA, and finally The data information of the corresponding sub-carrier can be obtained by demodulation by the demodulator.

The embodiment of the present invention has the following beneficial effects:

Solve the problem of carrier phase drift in high-speed multi-band PAM optical communication systems. Compared with other algorithms, the receiver does not need to know the specific order of the pulse amplitude modulation, and the phase offset can be determined without decoding after direct reception, which greatly reduces the computational complexity of the receiver.

It can be seen that those skilled in the art should understand that all or some of the steps in the methods disclosed above, the functional modules/units in the system, and the device can be implemented as software (which can be implemented by computer program codes executable by a computing device). ), firmware, hardware, and their appropriate combination. In a hardware implementation, the division between functional modules/units mentioned in the above description does not necessarily correspond to the division of physical components; for example, one physical component may have multiple functions, or one function or step may be composed of several physical components Components execute cooperatively. Some or all physical components may be implemented as software executed by a processor, such as a central processing unit, digital signal processor or microprocessor, or as hardware, or as an integrated circuit, such as an application specific integrated circuit .

In addition, communication media typically embodies computer readable instructions, data structures, computer program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism, and can include any information delivery, as is well known to those of ordinary skill in the art medium. Therefore, the present invention is not limited to any particular combination of hardware and software.

The above content is a further detailed description of the embodiments of the present invention in combination with specific embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deductions or substitutions can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (10)

1. A blind carrier phase shift compensation method in a Pulse Amplitude Modulation (PAM) system comprises the following steps:

decomposing the PAM signal of each subcarrier into a first real part signal and a first imaginary part signal;

respectively filtering the first real part signal and the imaginary part signal to obtain a second real part signal and a second imaginary part signal;

calculating a phase shift from the second imaginary signal and the second real signal;

the subcarrier frequency is compensated for according to the phase shift.

2. The blind carrier phase shift compensation method of claim 1 wherein said decomposing the PAM signal for each subcarrier into a first real component signal and a first imaginary component signal comprises:

multiplying the PAM signal by a cosine function cos (2 pi ft) to obtain a first real part signal;

multiplying the PAM signal by a sine function sin (2 pi ft) to obtain the first imaginary part signal;

the frequency in the cosine function and the frequency in the sine function are both equal to the frequency in the PAM signal.

3. The blind carrier phase shift compensation method of claim 1, wherein the filtering the first real part signal and the imaginary part signal respectively comprises:

and filtering signals in a preset frequency range in the real part signal and the imaginary part signal by a low-pass filter.

4. The blind carrier phase shift compensation method of claim 1 wherein said calculating a phase shift from said second imaginary signal and said second real signal comprises:

the phase shift is calculated using the following equation:

wherein,

for phase shifting, Q '(k) is the second imaginary signal, I' (k) is the second real signal, and k is the length of the transmitted symbol in the subcarrier.

5. The blind carrier phase shift compensation method of claim 1 wherein said calculating a phase shift from said second imaginary signal and said second real signal further comprises:

the phase shift is calculated using the following equation:

wherein,

for phase shifting, Q '(K) is the second imaginary signal, I' (K) is the second real signal, K is the length of the transmission symbol in the subcarrier, and K is the total length of the transmission symbol in the subcarrier.

6. A blind carrier phase shift compensation apparatus in a PAM system, comprising:

a signal decomposition module for decomposing the PAM signal of each subcarrier into a first real part signal and a first imaginary part signal;

the filtering module is used for respectively filtering the first real part signal and the imaginary part signal to obtain a second real part signal and a second imaginary part signal;

a phase shift calculation module for calculating a phase shift according to the second imaginary part signal and the second real part signal;

and the phase shift compensation module is used for compensating the carrier frequency according to the phase shift.

7. The blind carrier phase shift compensation apparatus of claim 6 wherein the decomposing the PAM signal for each subcarrier into a first real part signal and a first imaginary part signal comprises:

multiplying the PAM signal by a cosine function cos (2 pi ft) to obtain a first real part signal;

multiplying the PAM signal by a sine function sin (2 pi ft) to obtain the first imaginary part signal;

the frequency in the cosine function and the frequency in the sine function are both equal to the frequency in the PAM signal.

8. The blind carrier phase shift compensation apparatus of claim 6, wherein the filtering the first real part signal and the imaginary part signal respectively comprises:

and filtering signals in a preset frequency range in the real part signal and the imaginary part signal by a low-pass filter.

9. The blind carrier phase shift compensation apparatus of claim 6 wherein said calculating a phase shift from the second imaginary signal and the second real signal comprises:

the phase shift is calculated using the following equation:

wherein,

for phase shifting, Q '(k) is the second imaginary signal, I' (k) is the second real signal, k is in subcarrierThe length of the transmission symbol.

10. The blind carrier phase shift compensation apparatus of claim 6 wherein said calculating a phase shift from said second imaginary signal and said second real signal further comprises:

the phase shift is calculated using the following equation:

wherein,

for phase shifting, Q '(K) is the second imaginary signal, I' (K) is the second real signal, K is the length of the transmission symbol in the subcarrier, and K is the total length of the transmission symbol in the subcarrier.

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